The present invention relates to a method for recording information on a memory such as a so-called PC card provided with a semiconductor memory.
A tape recorder which uses such principle that information causes variation in magnetization has been widely used for recording audio information. Recently, there has been known and actually used another recording system using a memory card. The memory card, which is often referred to as a PC card, is provided with a semiconductor memory and has a size about a calling card.
The PC card comprises integrated elements such as the semiconductor memory, transistors, capacitors, and resistors. The semiconductor memories can be roughly categorized into a bipolar memory and a MOS memory. The bipolar memory is more advantageous than the MOS memory in that it requires less access time. However, larger power is consumed, and in addition, causes a larger heat radiation. To the contrary, the MOS memory requires a longer access time, but involves less power consumption and heat radiation. The semiconductor memory with a large capacity is usually a MOS memory.
Referring to FIG. 7, a conventional recording and reproducing system for the PC card comprises a CPU 1, audio interface 2, key interface 3, display interface 4, and a memory card interface 5. The audio interface 2 is applied with digital audio information through a DIR 7, and analog audio information through an A/D converter 8. The digital information is transmitted from the recording and reproducing system through a D/A converter 9. The key interface 3 is connected with a key matrix 10 for the user to input various information, and the display interface 4 is connected to a liquid crystal display 11 on which various information is shown. A PC card 12 is detachably connected to the memory card interface 5 so that the desired information is recorded on the card and read out therefrom. The information may further be erased from the PC card 12. The CPU 1 and the interfaces 2 to 5 are connected to each other through a system bus 6, and the interfaces 2 to 5 are connected to respective peripheral equipments 7 to 12 through the system buses 6.
The recording and reproducing system is further provided with a ROM 13 and a RAM 14. The ROM 13 stores a program for controlling the operation of the entire system. When the power of the system is turned on, the program in the ROM 13 is stored in the RAM 14 which is a main memory, thereby starting a predetermined operation. Namely, the interfaces 2 to 5 are initialized and the operations thereof checked. Hence the system is ready for operation which is started by operating the key matrix 10.
In operation, when a predetermined switch is turned on, the CPU 1 executes the program stored in the ROM 13. Information applied through the audio interface 2 is temporarily stored in the RAM 14, or in a separately provided buffer RAM, and thereafter, recorded on the PC card 12. The recorded information can be reproduced when a command signal is applied from the CPU 1. Various information is indicated on the display 11 during the operation.
In order to record a large quantity of information on the PC card 12, information may be compressed as necessary. The compressed information is directly recorded on the PC card 12. Alternatively, the uncompressed information corresponding to one block is stored in the RAM 14 or the buffer RAM, and thereafter, the block of information is compressed and written on the PC card 12. In the latter method, the compression and the recording are repeated until the necessary information are written on the PC card 12.
A compression factor at the compression is calculated as follows. When the sampling frequency when the information is not compressed is 48 kHz, which is the same as in the case of recording a digital audio tape (DAT), and one word corresponds to 16 bits, one channel bit rate (br) is 768 kbps/ch. Since EQU br=fs*w, EQU br=48 (kHz)*16 (bit)=768 kbps/ch
The equation applies to a case of a recording with one channel so that at a stereophonic recording, the value is doubled. Hence the compression factor is calculated in accordance with, EQU br=fs*w=M/2t
wherein M is the storage capacity of the PC card 12, and t is the recording time. The numeral 2 in the denominator indicates that the compression factor is applied to a stereophonic recording.
For example, when the PC card 12 has a storage capacity of 40 MB (10M word/stereophonic recording), the time capable of recording on the PC card at each compression factors is as follows. When the information is not compressed, the recording time is 208 sec/stereophonic recording. When the compression factor is 1/2, the recording time is 416 sec/stereophonic recording, when the compression factor is 1/3, 624 sec/stereophonic recording, and when 1/6, 1248 sec/stereophonic recording. The compression is carried out in accordance with various conventional methods which have been developed and used, so that the detailed descriptions thereof are omitted.
In such a recording and reproducing system, when the quantity of the information to be recorded, that is the length of recording time, is known beforehand, the user can select a PC card having a sufficient storage capacity, or determine an appropriate compression factor dependent on the storage capacity of the PC card. Hence, the information can be recorded from the beginning to the end without fail. However, when the length of the information is unknown, such as when recording every statement made during a conference, there may be cases where the conventional system cannot record the conference to the end. The entire conference can be recorded if a system using a large compression factor is employed. However, when the information is recorded at a large compression factor, the deterioration in sound quality inevitably occurs. Although the recording of a conference does not require a superior sound quality, the large compression factor may cause error at reproduction. Thus, it is preferable to maintain the compression factor as small as possible.
In addition, there may be a case where the recording time is unexpectedly short so that the PC card still has a large storage capacity left when the recording is over. Since the user do not think of using the same PC card when recording another information, the remaining storage capacity is wasted.
Namely, although there still may be a storage capacity left in the PC card, the user does not usually use the card when recording information of indefinite length. The user will use a new PC card instead. Hence in a system where the compression factor can be set at various levels, when the information is recorded at the largest compression factor, the length of the recording information may be unexpectedly short so that the storage capacity of the PC is wasted, which is undesirable. In order to prevent such a waste, the information on the PC card is re-recorded on another PC card so as to enable the information on the original PC card to be erased, or another information to be written over the old. Such an operation is troublesome.